The present invention relates to an expandable plug adapted to seal or to regulate pressure or flow within a tube, and also to a method of control.
Expandable plugs of this general type find application in cases where normal valving of flow is inappropriate for some reason, for example because the position of the desired seal or regulation is not fixed with respect to the tube, the desired seal is temporary, or the exterior of the tube is inaccessible.
The general approach to the design and construction of expandable plugs involves the use of an elastomeric cylinder or bladder, which is caused to increase in diameter. This may be done by a variety of mechanical means, or by application of internal pressure.
In use the plug will need to withstand diametral expansion and axial thrust, the latter being due to friction (in cases where the plug moves relative to the tube) and the differential tube fluid pressure across the plug.
Mechanically expanded plugs are suitable only for relatively small ratios of expansion and/or low axial thrusts. Larger expansion ratios may be required in cases for example where undue hydraulic obstruction of the tube cannot be tolerated when the plug is not expanded, or where the tube may vary in diameter or be caused to expand by fluid pressure behind the plug. For such applications, expansion by internal pressure is preferred.